Method for manufacturing an optical fiber

Abstract

A method of manufacturing an optical fiber, including: heating an optical fiber preform and drawing a glass fiber; measuring an outer diameter of the glass fiber as a function of time; transforming the function of time into a function of frequency; in the function of frequency, identifying a first peak due to a first drawing condition and a second peak due to a second drawing condition; and adjusting the second drawing condition so that fn < fm - wm / 2 or fn > fm + wm / 2 when a frequency of the first peak is set as fm, a full width at half maximum of the first peak is set as wm, and a frequency of the second peak is set as fn.

Description

[0001] Cross Reference To Related Applications

[0002] This patent application claims priority based on Japanese Patent Application No. 2020-117240 filed on July 7, 2020, and all the descriptions recited in the Japanese Patent Application are incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to a method for manufacturing an optical fiber. BACKGROUND

[0004] It is known that vibration of a drawing tower is one of the main causes of deterioration of variation in the glass outer diameter of an optical fiber. Japanese Patent Application Publication No. 2016-79073 describes a method in which a vibration suppression mechanism having a time constant of 1 second or less is provided between the drawing tower and an optical fiber preform, thereby suppressing variation in the glass outer diameter of the optical fiber caused by vibration of the drawing tower. SUMMARY

[0005] The method for manufacturing an optical fiber of the present application includes: heating an optical fiber preform and drawing a glass fiber; measuring the outer diameter of the glass fiber as a function of time; converting the function of time into a function of frequency; in the function of frequency, identifying a first peak caused by a first drawing condition and a second peak caused by a second drawing condition; and when the frequency of the first peak is set as fm, the full width at half maximum of the first peak is set as wm, and the frequency of the second peak is set as fn, adjusting the second drawing condition so that fn < fm - wm / 2 or fn > fm + wm / 2 is satisfied. BRIEF DESCRIPTION OF DRAWINGS

[0006] Figure 1 is a configuration view of a manufacturing apparatus used in the method for manufacturing an optical fiber to which the embodiments relate.

[0007] Figure 2 is a view obtained by viewing a swing guide roll from an upstream side of a route.

[0008] Figure 3 is a flowchart showing the method for manufacturing an optical fiber to which the embodiments relate.

[0009] Figure 4 is a flowchart showing a process of controlling swing of a swing guide roll.

[0010] Figure 5 is a view showing a time change in variation in the glass outer diameter in a case where the variation in the glass outer diameter is deteriorated.

[0011] Figure 6 is a view showing a frequency spectrum of variation in the glass outer diameter in a case where the variation in the glass outer diameter is deteriorated.

[0012] Figure 7 is a graph showing a frequency spectrum of the variation in the outer diameter of the glass in a case where feedback control is performed by the control section.

[0013] Figure 8 is a graph showing a time variation in the outer diameter of the glass in a case where feedback control is performed by the control section. DETAILED DESCRIPTION

[0014] [Problem to be Solved by the Invention]

[0015] As one of important characteristics of an optical fiber, polarization mode dispersion (PMD) can be cited. In Japanese Patent Application Publication No. 8-295528, a method is described in which a twist is applied to an optical fiber by periodically oscillating a guide roller, thereby suppressing PMD. However, in the method described in Japanese Patent Application Publication No. 8-295528, the outer diameter of the glass varies due to a change in the position and distance of the optical fiber. Moreover, under certain conditions, the variation in the outer diameter of the glass sometimes particularly deteriorates. In this case, in order to suppress the variation in the outer diameter of the glass, a method of greatly reducing the drawing speed or minimizing the applied twist, or the like, can be employed. However, productivity and yield are greatly impaired. According to the method described in Japanese Patent Application Publication No. 2016-79073, the variation in the outer diameter of the glass is improved to some extent, but is not sufficient.

[0016] An object of the present application is to provide a method of manufacturing an optical fiber that can further suppress the variation in the outer diameter of the glass without impairing productivity and yield.

[0017] [Effects of the Invention]

[0018] According to the present application, a method of manufacturing an optical fiber that can further suppress the variation in the outer diameter of the glass without impairing productivity and yield can be provided.

[0019] [Explanation of Embodiments of the Invention]

[0020] First, an embodiment of the present application is cited and explained. One embodiment of the present application relates to a method of manufacturing an optical fiber, including: heating an optical fiber precursor and drawing a glass fiber; measuring the outer diameter of the glass fiber to obtain a function of time; transforming the function of time into a function of frequency; in the function of frequency, identifying a first peak due to a first drawing condition and a second peak due to a second drawing condition; and when the frequency of the first peak is set to fm, the full width at half maximum of the first peak is set to wm, and the frequency of the second peak is set to fn, adjusting the second drawing condition so that fn < fm - wm / 2 or fn > fm + wm / 2 is satisfied.

[0021] In the manufacturing method of the optical fiber, the second peak due to the second drawing condition can be made not to overlap with the first peak due to the first drawing condition by adjusting the second drawing condition. Thus, a large amplitude due to the overlap of the first peak and the second peak can be suppressed. Therefore, the deterioration of the variation of the outer diameter of the glass can be further suppressed without deteriorating the productivity and the yield.

[0022] The sampling interval of the outer diameter can be 100 ms or less. In this case, the short-period variation of the outer diameter of the glass can be reliably detected.

[0023] The manufacturing method of the optical fiber described above can further include forming a coating layer on the glass fiber to be the optical fiber, and applying a twist to the optical fiber using a wobble guide roller. In this case, in order to apply the twist to the optical fiber, the wobble guide roller needs to be wobbled, and the wobble frequency of the wobble guide roller becomes the second drawing condition, thereby obtaining the second peak due to the wobble frequency. Thus, the first peak and the second peak can be more effectively made not to overlap with each other.

[0024] The second drawing condition can be the wobble frequency of the wobble guide roller. In this case, by adjusting the wobble frequency of the wobble guide roller, the deterioration of the variation of the outer diameter of the glass can be further suppressed without deteriorating the productivity and the yield.

[0025] [Detailed Description of Embodiments]

[0026] A specific example of the manufacturing method of the optical fiber of the present application will be described below with reference to the accompanying drawings. Note that the present application is not limited to these examples, but is represented by the scope of the claims, and is intended to include all variations within the meaning and scope equivalent to the claims. In the description of the drawings, the same symbols are attached to the same elements, and repeated description is omitted.

[0027] (Manufacturing Apparatus of Optical Fiber)

[0028] Figure 1 is a configuration view of a manufacturing apparatus used in the manufacturing method of the optical fiber to which the embodiments relate. Figure 1 The manufacturing apparatus 100 (drawing machine) illustrated is an apparatus for manufacturing an optical fiber 110 from an optical fiber preform 101 via a glass fiber 104. The manufacturing apparatus 100 is provided with a holding portion 102, a heating furnace 103, a holding furnace 105, a measurer 106, a cooler 107, a mold 108, an ultraviolet irradiator 109, a wobble guide roller 111, a capstan 112, a winding machine 113, and a control portion 114.

[0029] The holding section 102 holds the optical fiber preform 101 and feeds it into the heating furnace 103 at a certain speed. The optical fiber preform 101 has a base end section 101a held by the holding section 102 and a front end section 101b inserted into the inside of the heating furnace 103. The holding section 102 has a function of supplying the optical fiber preform 101 into the heating furnace 103.

[0030] The heating furnace 103 has an opening 103a into which the optical fiber preform 101 is inserted and an opening 103b opposite to the opening 103a and from which the glass fiber 104 is drawn out. The heating furnace 103 heats the front end section 101b of the optical fiber preform 101 supplied into the inside of the heating furnace 103 to soften it. The glass fiber 104 is drawn out from the front end section 101b softened by the heating, via the opening 103b, to the outside of the heating furnace 103.

[0031] The holding furnace 105 holds the glass fiber 104 to relax the structure of the glass. The measurer 106 measures the outer diameter of the glass fiber 104 in a state where the structure of the glass is relaxed (glass outer diameter). The measurer 106 measures the glass outer diameter, for example, by irradiating laser light to the glass fiber 104. The time interval of the sampling of the glass outer diameter by the measurer 106 is, for example, 100 ms or less. Although it also depends on the drawing speed, when the sampling interval becomes long, it can not be possible to detect the short-period variation of the glass outer diameter. The measurer 106 transmits the measured glass outer diameter to the control section 114.

[0032] The cooler 107 is arranged after the measurer 106 to cool the glass fiber 104. The mold 108 applies resin to the outer peripheral surface of the glass fiber 104 fed in to form a coated resin. The resin contains an acrylate-based ultraviolet-curable resin. The ultraviolet irradiator 109 irradiates ultraviolet light to the coated resin formed on the glass fiber 104 to cure the coated resin. Thus, the glass fiber is coated with the resin to form an optical fiber 110.

[0033] The wobble guide roller 111 applies twist to the optical fiber 110 by periodically inclining the axis direction. The wobble guide roller 111 is electrically connected to the control section 114, and twist is applied to the optical fiber 110 by controlling the wobble with the control section 114. A pair of fixed guide rollers can also be arranged before and after the wobble guide roller 111, but it is not possible to completely suppress the transmission of the wobble of the wobble guide roller 111 to other parts.

[0034] Figure 2 is a view of the wobble guide roller viewed from the upstream side (ultraviolet irradiator side) of the line. As Figure 2As shown, the swing guide roller 111 swings within a range of ±θ of the angle formed by the rotational axis M1 of the swing guide roller 111 and the predetermined axis M2. As a result of the swinging motion of the swing guide roller 111, when the rotational axis M1 of the swing guide roller 111 is inclined by an angle +θ with respect to the predetermined axis M2, a force in the lateral direction is applied to the optical fiber 110, the optical fiber 110 rolls on the surface of the swing guide roller 111, and thus a twist is applied to the optical fiber 110. When the swing guide roller 111 is inclined by an angle -θ with respect to the predetermined axis M2, a twist in the opposite direction is applied to the optical fiber 110.

[0035] That is, by repeatedly performing the symmetrical to-and-fro motion of swinging the swing guide roller 111 by an angle ±θ with respect to the predetermined axis M2, a clockwise twist and a counterclockwise twist with respect to the advancing direction (drawing direction) can be alternately applied to the optical fiber 110. Thus, the swing guide roller 111 guides the optical fiber 110 to the capstan 112 while applying a twist to the optical fiber 110.

[0036] The capstan 112 pulls the optical fiber 110 at a predetermined speed and tension. The winder 113 winds the optical fiber 110 pulled by the capstan 112. The control section 114 receives the glass outer diameter measured by the measurer 106 from the measurer 106, and performs feedback control of the swinging of the swing guide roller 111 on the basis of the glass outer diameter. The control section 114 can also control the entire manufacturing apparatus 100.

[0037] The control section 114 can be configured as, for example, a computer system including a processor such as a CPU (Central Processing Unit), a memory such as a RAM (Random Access Memory) and a ROM (Read Only Memory), an input / output device such as a touch panel, a mouse, a keyboard, a display, and a communication device such as a network card. The control section 114 causes each hardware to act under the control of the processor on the basis of a computer program stored in the memory, and thus functions of the control section 114 are realized.

[0038] (Method of manufacturing optical fiber)

[0039] Figure 3is a flowchart showing a manufacturing method of an optical fiber to which the embodiment is applied. The manufacturing method of the optical fiber 110 includes a step S1 of inserting an optical fiber preform 101 into a heating furnace (drawing furnace) 103, a step S2 of heating a front end portion 101b of the optical fiber preform 101, a step S3 of drawing a glass fiber 104 from the front end portion 101b, a step S4 of heat-insulating the glass fiber 104, a step S5 of measuring an outer diameter of the glass fiber 104, a step S6 of cooling the glass fiber 104, a step S7 of forming a coating layer on the glass fiber 104 to become the optical fiber 110, a step S8 of applying a twist to the optical fiber 110, and a step S9 of winding the optical fiber 110. Note that the steps S4 and subsequent steps are shown in order with a focus on a certain point in the length direction of the optical fiber 110.

[0040] In the step S1, the optical fiber preform 101 is inserted into the inside of the heating furnace 103 at a certain speed by the holding portion 102. With the base end portion 101a being held, the front end portion 101b of the optical fiber preform 101 is sent into the inside of the heating furnace 103 via the opening 103a of the heating furnace 103. In the step S2, the front end portion 101b is heated by the heating furnace 103 to be softened.

[0041] In the step S3, the glass fiber 104 is drawn from the front end portion 101b that is softened by heating via the opening 103b. The insertion speed of the optical fiber preform 101 in the step S1 can be set according to the drawing speed (drawing speed) of the glass fiber 104 in the step S3.

[0042] In the step S4, the drawn glass fiber 104 is heat-insulated by the heat-insulating furnace 105. Thereby, the structure of the glass can be relaxed. In the step S5, the outer diameter of the glass fiber 104 is measured by the measurer 106. In the step S6, the glass fiber 104 is cooled.

[0043] In the step S7, first, a coating resin is applied to the outer peripheral surface of the glass fiber 104 by the mold 108 to form a coating resin. Next, the coating resin is cured by ultraviolet rays irradiated from the ultraviolet ray irradiator 109, thereby becoming a coating layer that covers the glass fiber 104. Thereby, the coating layer is formed on the outer peripheral surface of the glass fiber 104. As a result, the optical fiber 110 is obtained. By repeating the step S7, a multilayer coating layer can also be formed.

[0044] In the step S8, a twist is applied to the optical fiber 110 by periodic oscillation of the oscillating guide roller 111. In the step S9, the optical fiber 110 is pulled at a predetermined speed and tension by the capstan 112, and then wound by the winder 113.

[0045] Figure 4is a flowchart showing a procedure of controlling the swing of the swing guide roller. The manufacturing method of the optical fiber 110 further includes Figure 4 The procedure S10 is a procedure of controlling the swing of the swing guide roller 111 based on the glass outer diameter measured in the procedure S5. The procedure S10 is performed by the control section 114. The control section 114 first performs a procedure S11 of acquiring the glass outer diameter. Specifically, the control section 114 receives the glass outer diameter measured in the procedure S5 from the measurer 106.

[0046] Next, the control section 114 performs a procedure S12 of recording the acquired glass outer diameter as a function of time. The control section 114, for example, stores the outer diameter in the memory in correspondence with the time. Next, the control section 114 performs a procedure S13 of transforming the recorded function into a function of frequency. The transformation is performed by Fourier transform.

[0047] Next, the control section 114 performs a procedure S14 of identifying the first peak Pl caused by the first drawing condition and the second peak P2 caused by the second drawing condition in the transformed function of frequency. The first drawing condition is, for example, the number of vibrations caused by vibrations of the manufacturing apparatus 100, a building, or the optical fiber preform 101. Here, the first drawing condition is the natural vibration frequency of the manufacturing apparatus 100. The second drawing condition is the frequency caused by external disturbances such as the swing frequency of the swing guide roller 111. The first peak Pl has a wide bandwidth. The second peak P2 has a narrower bandwidth than the first peak Pl.

[0048] Since the second peak P2 is a peak corresponding to the swing frequency of the swing guide roller 111 or a multiple thereof, the control section 114 can identify the second peak P2 based on the swing frequency of the swing guide roller 111. If the second peak P2 is identified, the control section 114 can identify the first peak Pl by comparison of the bandwidth of the second peak P2. Instead of the bandwidth, the full width at half maximum can be used for the comparison.

[0049] Next, in a case where the frequency of the first peak Pl is set to fm, the full width at half maximum of the first peak Pl is set to wm, and the frequency of the second peak P2 is set to fn, the control section 114 performs a procedure S15 of adjusting the second drawing condition so that fn< fm-wm / 2 or fn> fm+wm / 2 is satisfied. Since the second peak P2 corresponds to the frequency of the swing guide roller 111 or a multiple thereof, there are a plurality of second peaks P2. Thus, the second drawing condition can be adjusted so that the frequency fn of each of the second peaks P2 satisfies the above relation.

[0050] In the present embodiment, the control section 114 adjusts the oscillation frequency of the oscillating guide roller 111 as the second drawing condition. Thereby, the second peak P2 can be deviated from the first peak Pl so as not to overlap with the first peak Pl. As a result, the amplitude of the glass outer diameter variation can be suppressed from increasing due to the first peak Pl and the second peak P2 overlapping with each other. Here, the second peak P2 overlapping with the first peak Pl means that the frequency fn of the second peak P2 is within a frequency range centered on the frequency fm of the first peak Pl and having the same width as the full width at half maximum wm.

[0051] As described above, by the process S10 performed by the control section 114, the oscillation of the oscillating guide roller 111 can be controlled. The natural vibration frequency of the manufacturing apparatus 100 also varies depending on the excess length of the optical fiber preform 101. Therefore, once the second peak P2 is deviated from the first peak Pl by the process S10, the first peak Pl sometimes also varies to overlap with the second peak P2 again. Therefore, in the manufacture of the optical fiber 110, it is effective to always monitor the glass outer diameter and repeatedly perform the process S10 to perform feedback control of the second drawing condition. For example, the process S10 can be performed when the process S5 is performed at predetermined intervals, or the process S10 can be performed at predetermined time intervals.

[0052] Figure 5 is a graph showing the time variation of the glass outer diameter variation in the case where the glass outer diameter variation deteriorates. Figure 5 The horizontal axis of the graph ofrepresents time, and the vertical axis represents the glass outer diameter variation (pm). The glass outer diameter variation means the difference from the target value of the glass outer diameter. In a general optical fiber, the target value of the glass outer diameter is set to 125 pm. In Figure 5 In the graph of , the 3σ of the glass outer diameter variation is 0.41 pm.

[0053] Figure 6 is a graph showing the frequency spectrum of the glass outer diameter variation in the case where the glass outer diameter variation deteriorates. Figure 6 is a result obtained by performing Fourier transform on the time variation of the glass outer diameter variation shown in Figure 5 Figure 6 The horizontal axis of the graph of represents frequency, and the vertical axis represents intensity. In Figure 6 In the frequency spectrum shown in , there are the first peak Pl having a wide bandwidth and the second peak P2 having a narrow bandwidth. As described above, the first peak Pl is from the natural vibration frequency of the manufacturing apparatus 100. The second peak P2 corresponds to the frequency of the oscillating guide roller 111 to which the twist is applied or a multiple of half thereof. Here, the first peak Pl overlaps with one second peak P2. In this way, when the first peak Pl and the second peak P2 overlap with each other, the amplitude of the glass outer diameter variation increases.

[0054] Therefore, feedback control is performed by the control section 114. Figure 7 is a graph showing the frequency spectrum of the glass outer diameter variation in the case where feedback control is performed by the control section.Figure 7 The horizontal axis of the graph indicates frequency, and the vertical axis indicates intensity. Specifically, the frequency of the second peak P2 is adjusted so that the frequency of the second peak P2 is offset from the frequency of the first peak PI. When the oscillation frequency of the oscillating godet 111 is lowered, the frequency interval between adjacent second peaks P2 becomes narrow, and thus the second peak P2 easily overlaps with the first peak PI. Therefore, here, adjustment to increase the oscillation frequency of the oscillating godet 111 is performed.

[0055] Figure 8 is a graph indicating the time variation of the glass outer diameter variation when feedback control is performed by the control section. Figure 8 The horizontal axis of the graph indicates time, and the vertical axis indicates glass outer diameter variation (pm). In Figure 8 In the graph of FIG. 10, the 3σ improvement of the glass outer diameter variation is 0.22 pm. Note that the drawing speed was not changed. Therefore, the glass outer diameter variation was improved while productivity was maintained.

[0056] As described above, in the manufacturing method according to the embodiment, in the process S10, the second drawing condition is adjusted so that the first peak PI caused by the first drawing condition and the second peak P2 caused by the second drawing condition do not overlap with each other. Therefore, a large amplitude caused by the overlap of the first peak PI and the second peak P2 can be suppressed. Thus, the deterioration of the glass outer diameter variation can be further suppressed, and productivity and yield can not be deteriorated.

[0057] The sampling interval of the glass outer diameter by the measuring device 106 is 100 ms or less. Thus, a short-period variation of the glass outer diameter can be reliably detected.

[0058] The above manufacturing method includes a process S8 of forming a cladding layer on the glass fiber 104 to become an optical fiber 110, and then applying twist to the optical fiber 110 using the oscillating godet 111. Therefore, in order to apply twist to the optical fiber 110, the oscillating godet 111 needs to be oscillated, and thus the oscillation frequency of the oscillating godet 111 becomes the second drawing condition. Thus, the second peak P2 is obtained due to the oscillation frequency. Therefore, the process S10 of not overlapping the first peak PI and the second peak P2 with each other becomes more effective.

Claims

1. A method for manufacturing an optical fiber, comprising: heating a base material of the optical fiber and drawing glass fibers; measuring an outer diameter of the glass fibers to obtain a function of time; transforming the function of time into a function of frequency; identifying, in the function of frequency, a first peak caused by a first drawing condition and a second peak caused by a second drawing condition; when setting the frequency of the first peak as fm, the full width at half maximum of the first peak as wm, and the frequency of the second peak as fn, adjusting the second drawing condition such that fn < fm - wm / 2 or fn > fm + wm / 2 is satisfied; forming a coating layer on the glass fibers to form an optical fiber; and applying twisting to the optical fiber using a swing guide roller, a control unit receives the measured outer diameter of the glass fibers and performs feedback control on the swing of the swing guide roller based on the outer diameter of the glass fibers, the first drawing condition is the natural vibration frequency of a manufacturing apparatus, the second drawing condition is the swing frequency of the swing guide roller.

2. The method for manufacturing an optical fiber according to claim 1, wherein a time interval of sampling of the outer diameter is 100 ms or less.

3. The method for manufacturing an optical fiber according to claim 1, wherein the second peak includes a plurality of second peaks corresponding to the swing frequency of the swing guide roller or a half multiple thereof, adjusting the second drawing condition such that the frequency fn of each of the plurality of second peaks satisfies fn < fm - wm / 2 or fn > fm + wm / 2.

4. The method for manufacturing an optical fiber according to claim 1, wherein a bandwidth of the first peak is greater than a bandwidth of the second peak.

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